1. Field of the Invention
The present invention generally relates to networks using the IP (Internet Protocol), and more particularly, to a control executed when a congestion occurs in the network.
2. Description of the Related Art
Recently, the importance of IP data communications has been increased because of rapid popularization of personal computers, the Internet, active installation of intra-networks, and integration of voice and data on the IP (VoIP). Further, the networks themselves have had advanced functions and performance, and various applications have come into wide use. Examples of applications are electronic mail, WWW and reproduction of moving images and audio sound.
The arrangement of the network infrastructure actually makes it possible to increasingly transfer a variety of data on the IP. It is now expected that data communications (IP communications) will continuously come into wider use. On the other hand, there is a serious problem to be solved in the entire data communications. Such a problem relates to congestion control.
The congestion control function depends on a slow start algorithm of TCP/IP (Transmission Control Protocol/Internet Protocol) installed at each end system in IP communications. That is, the congestion control or congestion avoidance control has not been established in network sections of the infrastructure. Therefore, routing control directed to avoiding a congested route is not performed in the network at all.
The congestion control function performed at the end system is illustrated in FIG. 1. Referring to this figure, the TCP/IP recognizes that a related network may be too slow and starts operating. At the commencement of the congestion control, the transmitter sends a minimum packet, namely, a single packet. Then, the transmitter gradually increases the number of packets to be sent. If a packet is discarded due to a congestion in the network, and therefore an acknowledgement (ACK) has not been sent back, the transmitter drastically reduces the number of packets to be sent, and gradually increases the number of packets again. In the worst case in the above control, the TCP module of the end system sets the number of packets to zero and then increases the number of packets gradually in order to dissolve the congestion in the network. Therefore, the number of packets may be reduced on the sender side even if the network is not congested or another normal route is available at the time of reducing the amount of transmission. In addition, no algorithm of dynamically sending data over another route is neither available in the TCP nor the network. Thus, communications do not take place efficiently.
Recently, IP data has been used for multimedia streaming of moving pictures and voice. Video data and voice data have a relatively large amount of data and are continuously sent for a long time. This may congest the route over a long period and may affect other data communications. Also, UDP (User Datagram Protocol) is used for multimedia data. The UDP does not have the function of retransmission and slow start. Therefore, there is a possibility that a large amount of data may be discarded when data passes through the congested network.
In order to solve the above problems, it is necessary to transfer data packets over a route that is not busy or congested. However, a technique of the above routing has not yet been established.
Further, the prior art does not provide any congestion avoiding technique in the network section. Thus, data may be routed via the shortest path even when data can be routed to another path which is not in the congested state. Thus, the entire network cannot be utilized efficiently.
As described above, the congestion control cannot be sufficiently achieved totally by only the TCP/IP based congestion control. In addition, data cannot be routed to an idle path, which prevents data communications from taking place efficiently and the entire network from being utilized efficiently.